e_, x 50. _B_, a few
cells from the margin, with one of the hairs.]

Much like _OEdogonium_, but differing in being branched, is the genus
_Bulbochaete_, characterized also by hairs swollen at the base, and
prolonged into a delicate filament (Fig. 16, _G_).

The highest members of the _Confervaceae_ are those of the genus
_Coleochaete_ (Fig. 17), of which there are several species found in
the United States. These show some striking resemblances to the red
seaweeds, and possibly form a transition from the green algae to the
red. The commonest species form bright-green discs, adhering firmly
to the stems and floating leaves of water lilies and other aquatics.
In aquaria they sometimes attach themselves in large numbers to the
glass sides of the vessel.

Growing from the upper surface are numerous hairs, consisting of a
short, sheath-like base, including a very long and delicate filament
(Fig. 17, _B_). In their methods of reproduction they resemble
_OEdogonium_, but the reproductive organs are more specialized.

CHAPTER V.

GREEN ALGAE--_Continued_.

ORDER III.--POND SCUMS (_Conjugatae_).

The _Conjugatae_, while in some respects approaching the _Confervaceae_
in structure, yet differ from them to such an extent in some respects
that their close relationship is doubtful. They are very common and
familiar plants, some of them forming great floating masses upon the
surface of every stagnant pond and ditch, being commonly known as
"pond scum." The commonest of these pond scums belong to the genus
_Spirogyra_, and one of these will illustrate the characteristics of
the order. When in active growth these masses are of a vivid green,
and owing to the presence of a gelatinous coating feel slimy, slipping
through the hands when one attempts to lift them from the water.
Spread out in water, the masses are seen to be composed of slender
threads, often many centimetres in length, and showing no sign of
branching.

[Illustration: FIG. 18.--_A_, a filament of a common pond scum
(_Spirogyra_) separating into two parts. _B_, a cell undergoing
division. The cell is seen in optical section, and the chlorophyll
bands are omitted, _n_, _n'_, the two nuclei. _C_, a complete cell.
_n_, nucleus. _py._ pyrenoid. _D_, _E_, successive stages in the
process of conjugation. _G_, a ripe spore. _H_, a form in which
conjugation takes place between the cells of the same filament. All
x 150.]

For microscopical examinatio